Help me choose my first AR15

Looking to buy my first AR and these are in my budget. On one hand I like the classic look of a standard M4 but I believe M-lok gives me more room for attachments?

Anything else I should know before I buy?

Looking to buy my first AR and these are in my budget. On one hand I like the classic look of a standard M4 but I believe M-lok gives me more room for attachments?

Anything else I should know before I buy?